Protein import into complex plastids

许多藻类在次生内共生中进化。在这里，含有被两层膜包围的质体的单细胞真核细胞被另一种真核生物内化。在这种细胞内细胞的共同进化过程中，光养细胞被还原为由三层或四层膜包围的复杂质体。从许多基因组计划可知，复杂质体的基因组不具备编码所有位于质体的蛋白质的能力。因此，对于共生相互作用，建立了运输系统以保证核编码质体蛋白穿过质体周围膜的运输。对于被四层膜包围的硅藻质体，我们首次鉴定了第二层膜的易位子，并且在一个合作项目中鉴定了第三层膜的易位子。此外，我们还表明这些易位子存在于许多其他藻类以及一些细胞内寄生虫中。在此应用的项目中，我们将重点关注第二最外膜中的易位复合物的相互作用因素及其结构。为此，我们将应用首先在二次进化的模型生物中使用的策略。此外，还计划确定重要易位复合物成分的蛋白质结构。我们期望从我们的工作中深入了解易位复合体及其功能。由于该复合体的膜成分与真核细胞的 ERAD 机制同源，因此我们预计从事 ERAD 工作的社区也将从我们的工作中受益。

Many algae evolved in secondary endosymbiosis. Here a unicellular, eukaryotic cell harboring a plastid surrounded by two membranes was internalized by another eukaryote. In the course of the co-evolution of this cell-within-a-cell the phototrophic cell was reduced to a complex plastid surrounded by either three or four membranes. From many genome projects it is known that the genomes of complex plastids have not the capacity to encode all plastid-located proteins. Thus, for the symbiontic interaction a transport system was established to guarantee transport of nucleus-encoded plastid protein across the plastid surrounding membranes. In case of the plastids of diatoms, which are surrounded by four membranes, we have identified for the first time the translocators of the second outermost and, in a cooperation project, of the third membrane. Additionally we have shown that these translocators are present in many other algae as well as in some intracellular parasites. In the project applied here, we will focus on the translocator complex in the second outermost membrane in respect to interacting factors and its structure. For that we will apply strategies firstly used in a secondarily evolved model organism. In addition it is planned to determine the protein structure of important translocator complex components. We expect from our work in-depth insights into the translocator complex and its functions. As this complex is in respect to its membrane components homologous to the ERAD machinery of eukaryotic cells, we expect that the community working on ERAD will profit from our work as well.